Navien NFC-175 Service Manual page 76

Check method
Failure mode
Ignition failure
Defective electrode gap
76 NFC Service Manual
Cause
1. Check if the main gas valve is open.
2. Check the gas supply pressure.
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3. Check the flexible pipe diameter for compatibility with the boiler.
4. While the static pressure is normal, the use of another gas appliance may cause a
possible drop in gas pressure to the unit. Therefore, it is required to check the dynamic
pressure.
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Gas supply error
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5. If a CSST connector has been used, check to ensure that it is not been over tightened
resulting in the seal obstructing gas flow.
6. Check the meter class. (Example)
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CFH = 1,020 BTU/h
Digital pressure
manometer
Check gas supply pressure (refer to page 21).
Defective electrode gap and shape disables ignition.
Appropriate electrode gap: approx. 3~4mm(1/8") (replace if defective)
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An ignition fail may occur due to improper gap, while discharge seems normal when
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and shape
checked via the flame monitoring window. Therefore, it is required to check the gap after
disassembly.
NG: 3.5" - 10.5" W.C, LP: 8" – 13.5" W.C
LP pressure drop occurs frequently in the winter.
Static pressure: Check the gas pressure at standby mode.
Dynamic pressure: Check the gas pressure at max combustion. (2nd stage MAX
combustion setting: DIP S / W 1-1 ON)
Gas meter Boiler Furnace Domestic gas stove
425 CFH (Gas Meter) ≥ 195 CFH (Boiler)+ 58.8 CFH (Furnace)
+ 63.7 CFH (Domestic gas stove)
Check method
A shifted seal narrows the inner diameter of
CSST connector
Version 1.0